Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02426253 2003-04-22
lgubber Reduction
Field of the Invention
S The invention generally relates to rubber reduction, and more particularly
to tire
reduction using a solvent at a subcritical temperature.
Background of the Invention
It is estimated that in many countries the number of used tires produced per
year
is approximately equal to the population of the country. As an example there
are more
than 250 million used tires produced annually in the United States. Methods of
dealing
with these used tires can generally be placed in two categories i.e. disposal
and
reclamation. The former group includes land filling and stock pilling which
are
increasingly unacceptable options for a multitude of reasons. Within the
latter group are
approaches that use the tires in close to their original state with possibly
some physical
processing. Examples within this group include vibration and debris dampening
mats as
may be used drilling operations or filler material for road construction. Most
of the
applications in this category represent a limited volume of tires and do not
exploit the
economic value of the material within the tire.
A second group of reclamation methods look to extracting value from the
constituent materials within a tire. Major constituents include synthetic and
natural
rubber, carbon black and steel. Minor constituents include sulphur that is
used for cross-
linking of the rubber chains during the vulcanization process. The most basic
reclamation alternative is the use of tires as a fuel. In this case the tire
may be in its
original unprocessed state or it may have been reduced to simpler hydrocarbons
such as
oils. This latter alternative is favourable as constituents that axe not
desirable during
burning would generally be removed. However, the use of tires as a fuel again
reduces
the value of the reclaimed material to a point where there is little or no
retention of value
added during the fabrication of the tire.
Therefore, there is a need for a method and system that provides for the
reclamation of tires while maintaining value added to the constituent
materials during the
original processing of the tire.
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Summary of the Invention
The invention is directed to a method and system for the reduction of tires.
An
object of the invention is to provide a system and method for the reduction of
tires to
hydrocarbons where at least a portion of these hydrocarbons have a molecular
weight that
is larger than oils.
Other aspects and advantages of the invention, as well as the structure and
operation of various embodiments of the invention, will become apparent to
those
ordinarily skilled in the art upon review of the following description of the
invention in
conjunction with the accompanying drawings.
Brief Description of the Drawings
The invention will be described with reference to the accompanying drawings,
wherein:
Fig. la is a schematic graph illustrating % completion v. time for a pyrolisis
reduction process;
Fig. lb is a schematic graph illustrating % completion v. time for a non-
pyrolisis
reduction process;
Fig. 2 is a flow chart of a process for reducing tires according to an
embodiment
of the invention;
Fig. 3 is a flow chart of a process for reducing tires according to another
embodiment of the invention; and
Fig. 4 is a flow chart of a process for reducing tires according to a further
embodiment of the invention.
Like numerals identify like features within the drawings.
Detailed Description of the Invention
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CA 02426253 2003-04-22
The reduction of tires can generally be considered to include two steps or
processes. The first of these is devulcanization where cross-linking sulphur
bonds
between rubber molecules are broken. At the end of the devulcanization process
the
mass of solid residue is approximately 100% of the original mass of tire. Th.e
solid
residue contains rubber hydrocarbon and carbon black where rubber hydrocarbon
includes any hydrocarbon originating from the initial rubber. The rubber
hydrocarbon
has an average molecular weight that is generally less than the initial rubber
and greater
than oil, where oil has an average molecular weight of approximately 500 or
less. The
depolymerization process reduces the average molecular weight of the rubber
hydrocarbon until, at completion, the rubber hydrocarbon is substantially oil.
The mass
of solid residue is approximately 40% of the initial mass of tire at the end
of the
depolymerization process. At this point the solid residue is substantially
only carbon
black.
1 S Figure 1 a is schematic graph of the % completion v. time for a normal
pyrolisis
process. In a normal pyrolisis process a devulcanization process102 and a
depolymerization process 104 occur substantially in parallel. As such the two
processes
are complete at approximately the same time i.e. tV~tp. Figure lb shows a non-
pyrolisis
process in which the devulcanization process 106 is separated from the
depolymerization
process 108. At time t~ the devulcanization process 106 is complete while the
depolymerization process 108 is only a fraction of the way to completion.
The process of reducing tires according to an embodiment of the invention
allows
for at least some separation of the devulcanization and a depolymerization
processes. A
flow chart of a reduction process according to an embodiment of the instant
invention is
presented in Figure 2. Tire feedstock is provided to a reactor suitable for
temperatures
and pressures appropriate for subcritical treatment with water at step 202.
Water is
provided to the reactor at step 204. The amount of water provided is
sufficient to
maintain the saturated water vapour pressure at the reaction temperature and
to allow the
tire feedstock to be immersed in the liquid water at the reaction temperature.
The reactor is heated to the reaction temperature at step 206. To maintain a
subcritical reaction the reaction temperature is less than the critical
temperature of water.
The reaction pressure is provided at step 208. This pressure is greater than
or equal to the
saturated water vapour pressure at the reaction temperature. In the current
embodiment
the reaction temperature is between about 280~aC and about 350°C and
the reaction
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CA 02426253 2003-04-22
pressure is between about 950 psig and about 2400 psig. The reaction is
continued at
step 210 for time t. In the current embodiment time t is less than about 1 hr.
A reaction
product is produced at step 212. The reaction product produced according to
the process
of the current embodiment includes devulcanized rubber hydrocarbon, carbon
black and
may include some oils resulting from at Least partial depolymerization of the
rubber
hydrocarbon.
A flow chart of a reduction process according to another embodiment of the
invention is presented in Figure 3. The pracess includes the steps presented
in Figure 2.
The process according to this embodiment of this invention. further includes
the step of
treating the reaction product with a solvent at step 302. In this embodiment
the solvent is
one appropriate for the dissolution of rubber hydrocarbon, including toluene
and
cyclohexane. The use of other solvents and mixtures of solvents as appropriate
for the
dissolution of the reaction product, which may include hydrocarbons of varying
molecular weight will be apparent to one skilled in the art. Carbon black is
then
separated from the reaction product at step 304 using filtration methods. It
will be
apparent to one skilled in the art that any appropriate techniques may be
implemented for
the separation of the carbon black form the dissolved reaction product.
A flow chart of a reduction process according to a further embodiment of the
invention is presented in Figure 4. The process includes the steps presented
in Figure 3.
The process according to this embodiment of this invention further includes
the step of
separating the solvent from the rubber hydrocarbon. Techniques appropriate for
separating the solvent from the rubber hydrocarbon will be apparent to one
skilled in the
art. In this embodiment evaporation is used to separate the solvent from the
rubber
hydrocarbon.
Process parameters for subcritical fluid techniques include pressure,
temperature,
fluid or solvent and time. Without being bound by theory it appears that
operation of the
process at temperatures below the critical temperature of the solvent allows
for the
separation of the devulcanization and the depolymerization processes. The rate
of
depolymerization process is lowered to an extent where it is effectively
separated from
the step of devulcanization. This allows unproved control regarding the extent
to which
depolymerization is allowed to proceed. In an embodiment of the invention the
reaction
time is varied to provide substantially complete devulcanization and a desired
amount of
depolyrnerization.
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It will be apparent to one skilled in the art that tires can include any
vulcanized
rubber tire as may be used for transportation purposes. It will also be
apparent to one of
skill in the art that other vulcanized rubber, synthetic and natural, products
may be used
5 as a feedstock.
It will be further apparent to one of skill in the art that the processing
conditions
presented above are with respect to one embodiment of the invention. The
invention
encompasses those processing parameters i.e. temperature, pressure, time and
solvent that
allow for the separation of the devulcanization and depolymerization steps
within the
reduction process.
While the invention has been described according to what is presently
considered
to be the most practical and prefeaTed embodiments, it must be understood that
the
invention is not limited to the disclosed embodiments. Those ordinarily
skilled in the art
will understand that various modifications and equivalent structures and
functions may be
made without departing from the spirit and scope of the invention as defined
in the
claims. Therefore, the invention as defined in the claims must be accorded the
broadest
possible interpretation so as to encompass all such modifications and
equivalent
structures and functions.
